1. Technical Field of the Invention
The present invention generally relates to passive optical networks (“PONs”). More particularly, and not by way of any limitation, the present invention is directed to system and method for implementing fast layer 2 (“L2”) protection in PONs.
2. Description of Related Art
Wavelength Division Multiplex Passive Optical Networks (“WPONs”) rely on shared optical wavelength and unidirectional connections. Ethernet is used as the L2 technology in WPON. To prevent single point of failure, WPON employs dual-hub architecture; as a result, it is necessary to maintain a loop-free topology. However, the standard spanning tree cannot correctly function in such a network.
Currently, the solution to the foregoing problem is to utilize spanning tree protocols (“STP”) for providing both a loop-free network and protection. STP and the more recently developed rapid STP (“RSTP”) and multiple STP (“MSTP”) work efficiently in local area networks (LANS) and switched Ethernet networks for offering network protection at L2. This solution is deficient, however, in that bridges need bi-directional ports to exchange bridge protocol data units (“BPDUs”). Point-to-point connections are required to fully enable fast convergence. WPON is based on broadcast and shared optical bandwidth. Additionally, WPON nodes use asymmetric ports, i.e., some ports have only receivers, for efficient and cost effective data distribution. As a result, the broadcast and asymmetrical nature of the network prevents standard L2 protection schemes from functioning properly.
Therefore, what is needed is a system and method to provide L2 protection for networks that employ broadcast media and asymmetric traffic distribution.